How is uniform electric field produced?

[ehabmozart]

How is uniform electric field produced? Consider two parallel plates with one +ve and the other -ve. The field depends on the charge producing the field and the distance to a point in between the place. However, in this case, the distance decreases and hence the field decreases and is not constant... Kindly Explain and I am thankful!

 

[rcgldr]

Assuming the plates are large compared to the distance between them, then the plates can be treated as plates of infinite size, and the potential (voltage) changes with position, but the field between the plates remains constant.

For an explanation, you can start here:

http://hyperphysics.phy-astr.gsu.edu/%E2%80%8Chbase/electric/elesht.html#c2

and here for the field from a disc of radius R:

http://hyperphysics.phy-astr.gsu.edu/%E2%80%8Chbase/electric/elelin.html#c3

Note that for the disk of radius R, as R -> ∞ the field becomes independent of the distance z and become E = k σ 2 π . You can also use calculus to get the same result by considering a plane of infinite size to be composed of an infinite number of infinitly long charged lines (with fixed amount of charge per unit length) side by side.